The present invention relates to a paper feeder for use in printing machines which includes a separation suction device vertically movable for sucking one sheet at a time from sheets stacked on a stacking table and a transport suction device for feeding the sucked sheet horizontally into the printing machine.
Machines for handling sheets of paper, such as sheet-fed presses and sheet folding machines, include a paper feeder for drawing sheets of paper one at a time from a stack on a stacking table and feeding each sheet in the forward direction into the machine. Such known paper feeders include separation suction devices which are vertically movable, for sucking one sheet at a time, transport suction devices forwardly movable for feeding the picked-up sheet, an air blower for shuffling several uppermost sheets, and a probing foot for separating the sucked sheet from a next lower sheet on the sheet stack. The separation suction devices have suction nozzles which are positionally adjusted in advance so as to be inclined with respect to the direction of feed and a direction transverse thereto, and are upwardly movable in a direction at an angle to the vertical direction, so that the separation suction devices can correct the orientation of the sheet and keep the latter taut while moving upwardly. Such adjustment is time-consuming and requires a skillful operation and is normally repeated several times before proper adjustment is achieved, and results in an unwanted downtime of the printing machine. A device has been proposed for adjusting the separation suction devices while the printing machine is in operation. The proposed device, however, is large in size and complicated, cannot effect smooth adjustment, and tends to allow the separation suction devices to move unstably.
Complete paper feeding requires that the uppermost sheet be readily separated from the lower sheet, the picked-up sheet be removed easily from the suction nozzle when sucked by the transport suction devices, and various parts be moved smoothly to keep up with high-speed operation. Prior paper feeders, however, have failed to meet these requirements.
The probing foot is vertically adjustable to detect the level of the topmost sheet for adjusting the distance between the suction nozzle and the topmost sheet. Such an adjusting operation requires complete shutdown of the paper feeder device, and is tedious and time-consuming. The probing foot adjustment sometimes involves height adjustment of the paper feeder device to avoid poor sheet shuffling, resulting in a more complex adjusting procedure. According to an alternative arrangement, the separation suction devices are movable vertically relative to the level of the uppermost sheet. However, such adjustment also results in a downtime of the paper feeder and is time-consuming.